Physicians make use of catheters today in medical procedures to gain access into interior regions of the body to ablate targeted tissue areas. It is important for the physician to be able to precisely locate the catheter and control its emission of energy within the body during tissue ablation procedures.
The need for precise control over the catheter is especially critical during procedures that ablate endocardial tissue within the heart. These procedures, called electrophysiological therapy, are use to treat cardiac rhythm disturbances.
During these procedures, a physician steers a catheter through a main vein or artery into the interior region of the heart that is to be treated. The physician then further manipulates a steering mechanism to place the electrode carried on the distal tip of the catheter into direct contact with the endocardial tissue that is to be ablated. The physician directs energy from the electrode through tissue either to an indifferent electrode (in a unipolar electrode arrangement) or to an adjacent electrode (in a bi-polar electrode arrangement) to ablate the tissue and form a lesion.
Physicians examine the propagation of electrical impulses in heart tissue to locate aberrant conductive pathways and to identify foci, which are ablated. The techniques used to analyze these pathways and locate foci are commonly called "mapping."
Conventional cardiac tissue mapping techniques use multiple electrodes positioned in contact with epicardial heart tissue to obtain multiple electrograms. These conventional mapping techniques require invasive open heart surgical techniques to position the electrodes on the epicardial surface of the heart.
An alternative technique of introducing multiple electrode arrays into the heart through vein or arterial accesses to map endocardial tissue is known. Compared to conventional, open heart mapping techniques, endocardial mapping techniques, being comparatively non-invasive, hold great promise. Still, widespread practice of endocardial mapping techniques has been hindered by the difficulties of making suitable endocardial electrode support structures, including severe size constraints, strength and durability demands, and the sheer complexities of fabrication.
An endocardial mapping structure can potentially remain in place within a heart chamber for several thousand heart beats. During this time, the powerful contractions of heart muscle constantly flex and stress the structure. The structure must be strong and flexible enough to keep the electrodes spaced apart both longitudinally and circumferentially without failure and without shed parts. In addition, there is also the need to provide simple, yet reliable ways of electrically coupling multiple electrodes to external sensing equipment. Still, though strong and durable, the structures must cause no trauma when in contact with tissue.
While prior multiple electrode support structures may attempt to provided the requisite strength and flexibility, they have created envelopes with blunt, non-conforming contours that can poke into tissue and cause trauma during heart contractions.
It can be seen that providing economical, durable, and safe multiple electrodes in a package small enough to be deployed within the heart often poses conflicting challenges.